1. Field
Example embodiments relate to a two-block sensing system and more particularly a two-block sensing system attached to an end of a lifting device, for example, a crane.
2. Description of the Related Art
A crane, in its most basic form, is a machine for raising and lowering objects, and, while holding them suspended, transporting them through a limited lateral distance. In one form it consists of a projecting arm or jib or boom of timber or iron, a rotating post or base, and the necessary tackle, windlass, etc. The arm or jib or boom includes an end. This end is where cables, which are attached to a load, are threaded through a pulley block or sheaves. This end of the boom is what is referred to by many in the industry as the “horsehead”; this reference is for obvious visual reasons.
In a conventional crane, a first pulley block is arranged in the horsehead. A cable threaded through the first pulley block is also threaded through a second pulley block (known in the industry as a “snatch block”) which is associated with a hook. In the conventional art, the pulley block of a hook may be moved towards the horsehead. For example, when the boom telescopes outward (or is lowered) the pulley block associated with the hook will be pulled towards the horsehead. Alternatively, the hook's pulley block may be pulled towards the horsehead via an activation of a winch. A “two-block” condition occurs when the hook's pulley block runs into the boom's pulley block. Such a condition is to be avoided as the two-block condition may result in damage to the crane and/or its components. For example, in the event the hook's pulley block runs into the boom's pulley block, the cable could be snapped.
In the conventional art, two-block sensors are arranged at the horsehead in order to detect whether a collision between the hook's pulley block and the horsehead's pulley block is imminent. In the event the two-block sensors detect that a collision is imminent, the two-block sensors cause various operations of the crane to stop. For example, in some conventional cranes, the two-block sensor may cause the winch to cease operating.